Bussmann 300A Fast Acting Melamine Fuse with 600VAC Voltage Rating; JJS Series

Fast-acting, nonindicating UL Class T fuses open within seconds of being exposed to overloads and short circuits. Also called fast-blow Class T fuses, they are highly sensitive to changes in current flow and don't tolerate temporary overload currents or power surges. They have no indicator for identifying a blown fuse, so they're sometimes used with an indicating fuse block or cover.

UL Class T fuses are very small fuses that require minimal installation space for protecting electrical feeders and branch circuits from overcurrent. These fuses have an interrupting rating (IR) of 200kA and are not interchangeable with any other UL fuse class. They are current-limiting to prevent electrical damage by disconnecting circuits before they're exposed to the full magnitude and duration of an overcurrent.